From pre-puberty when they first knew they were different from when they realized they were Trans women. Then, from such realization and the steps they start to take to make themselves more feminine and attractive.
The overall journey to “complete” womanhood is long and challenging and involves regular medication and several surgeries. Most are very painful and uncomfortable so don’t let anyone ever tell you being Trans is a lifestyle choice. The pain and prejudices associated with being a Transgender woman are significant.